Phased array antenna panels are used to generate steerable beams that may be utilized in wireless communication systems. Phased arrays create a focused beam that can be steered very quickly to maintain a link for any on-the-move communication system. Conventional wireless communications systems can also utilize steerable beams to communicate with multiple wireless nodes by moving the beams from one wireless node to the next. A single beam may service multiple wireless nodes in a sequence and repeat the sequence periodically such that each wireless node appears to be in constant communications with the system. The beam steering is generally implemented by power amplifiers in the transceiver circuitry. The power amplifiers drive respective antenna elements of the phased antenna array to produce and steer the beams.
Generally, power amplifiers (PAs) are designed for maximum power transfer, and small signal output return loss is less of a concern. In general, power transfer is more important than small signal output return loss and the conventional PAs are connected to well-controlled loads like 50 Ohms. To achieve higher power transfer and efficiency, the PA should be in a non-linear mode (one way is Class-AB design). Having higher efficiency PAs means the output return loss will vary with power. The load of the PA is well known and does not change, therefore there is no concern about load change. For this reason, conventional PAs can be designed with poor output return loss (S22). In general, approximately −5/−7 dB return loss is acceptable while a very good matching requires less than −15 dB.
Phased array systems are more susceptible to output return loss because the output of each transceiver is connected to a respective antenna element on a phased array panel. Having 10+ or 100+ antennas on the same phased array panel leads to significant coupling between antennas. The coupling between the antennas results in different impedances for the respective PAs, especially when beam steering of the phased array is performed. Thus, for PAs in a phased array system it would be desirable to have a good output matching (return loss) as well as high output power. In addition, in fifth generation (5G) communication systems, where the PAs are operated in a back-off region (i.e., 3-8 dB back-off from output compression point), the PAs should have good output matching in different output power levels. As a result, a well matched output port is needed at the same time as highest power transfer.
It would be desirable to implement a method to improve PA output return loss and back-off performance with an RC feedback network.